1. Technical Field
The present invention relates to a display device having a pair of glass substrates and a method for cutting it. Specifically, the invention relates to a display device having a pair of glass substrates and a method for cutting it in which, when a glass substrate of a display device is cut by an internal scribing method, vertical movement of a scribing wheel is reduced to improve the cutting efficiency, and that is less prone to cracking, chipping, and waste residue.
2. Related Art
Thin display devices such as LCDs have a bonded glass substrate pair. A process for manufacturing such display devices having a bonded glass substrate pair includes a process for cutting a large glass substrate pair into separate pieces and a process for cutting off peripheral portions. In such cutting processes, there is generally used a process including forming a scribing groove (also called “scribing”) using, for example, a sintered diamond cutter (scribing wheel), and breaking. This known scribing and breaking process will be described with reference to FIGS. 8A to 8E.
FIGS. 8A to 8E are side views step by step illustrating the known scribing and breaking process.
A bonded glass substrate pair to be cut consists of a first glass substrate 51 and a second glass substrate 52. First, a scribing groove 54 is formed in the surface of the first glass substrate 51 using a scribing wheel 53 along a cutting line (FIG. 8A). Thereafter, the bonded glass substrate pair (51 and 52) is reversed and placed on a breaking table (not shown). A rubber roller 55 is pressed against the second glass substrate 52 at a position corresponding to the scribing groove 54. A crack 56 is thereby formed in the first glass substrate 51 from the scribing groove 54 (FIG. 8B). Next, a scribing groove 57 is formed in the surface of the second glass substrate 52 using the scribing wheel 53 along a cutting line (FIG. 8C). Thereafter, the bonded glass substrate pair (51 and 52) is reversed and placed on the breaking table. The rubber roller 55 is pressed against the first glass substrate 51 at a position corresponding to the scribing groove 57. A crack 58 is thereby formed in the second glass substrate 52 from the scribing groove 57 (FIG. 8D). In this way, the cracks 56 and 58 are formed in the bonded glass substrate pair (51 and 52). By removing portions 591 and 592 from the bonded glass substrate pair (51 and 52), a display panel 50 of a predetermined size is obtained (FIG. 8E).
Instead of the rubber roller 55, a breaking bar can be used in the breaking process (see JP-A-2003-131185).
In the scribing process, there is normally used a method in which scribing using a scribing wheel is performed throughout the length of a glass substrate (hereinafter referred to as “external cutting scribing method”). This external cutting scribing method is effective when the thickness of one of the pair of glass substrates is 0.3 mm or more. However, when the thickness of one of the pair of glass substrates is less than 0.3 mm (for example, 0.225 mm) as in display devices used in recent small mobile devices, using the above external cutting scribing method causes cracking and/or chipping at the start of scribing.
Therefore, in the case of scribing a thin glass substrate, there is used a scribing method in which scribing is performed inside the edge of a glass substrate by using a special scribing wheel (hereinafter referred to as “internal cutting scribing method”). This internal cutting scribing method is a method in which a head of a scribing machine is driven vertically so that a scribing wheel is lowered onto a portion inside the edge of a glass substrate, a scribing process is started, and thereafter the scribing wheel is raised before reaching the edge of the glass substrate. This internal cutting scribing method makes it possible to form a scribing groove without causing chipping even when the thickness of one of the pair of glass substrates is less than 0.3 mm.
In the case of the above-described external cutting scribing method, when the thickness of one of the pair of glass substrates is 0.3 mm or more, scribing grooves can be formed continuously in a plurality of glass substrates with the height of the scribing wheel held constant, without causing chipping. However, when the thickness of one of the pair of glass substrates is less than 0.3 mm, the external cutting scribing method is difficult to use because cracking and/or chipping occurs at the start of scribing.
In contrast, the internal cutting scribing method does not cause chipping at the start of scribing even when the thickness of one of the pair of glass substrates is less than 0.3 mm. However, since the portion between the edge of a glass substrate and the scribing start position is not scribed, the internal cutting scribing method is prone to waste residue. In addition, in order to form scribing grooves continuously in a plurality of glass substrates, it is necessary to repeat the processes of lowering the scribing wheel, forming a scribing groove, and raising the scribing wheel. Therefore, the capacity per unit time of the internal cutting scribing method is about 35% lower than that of the external cutting scribing method in which the height of the scribing wheel is held constant.